Inflation of a typical airbag cushion in a vehicle is achieved by igniting a propellant stored in an inflator. Once ignited, the propellant rapidly generates large volumes of gas which fill the airbag inflating the cushion to protect the vehicle occupants. These devices are credited for saving numerous lives in the event of a vehicle crash.
During the manufacture of these propellant filled inflators, special care is used to insure proper handling and safety precautions are followed to avoid inadvertent ignition of the propellant.
Once assembled, the inflators laden with propellant are moved to an assembly location wherein the inflator can be placed in a module housing along with the airbag cushion. In the case of a side curtain airbag, the inflator may be attached to a fill tube connected to a curtain airbag or directly to the cushion. Alternatively, the inflators could be boxed and stored for later assembly or shipment. In any event, large numbers of the inflators are routinely shipped and transported to vehicle assembly plants.
It is during storage and transportation that these propellant filled inflators can pose a risk in the event of an inadvertent ignition. The situation is generally remote, but in the event of a fire in shipping or storage, the propellant could be ignited causing a release of gases which could cause a condition of high thrust making the unrestrained inflator a projectile or missile causing a risk to personnel standing nearby or those trying to put out the fire.
As a result of this risk, the United States Department of Transportation requires inflators to be subjected to a bonfire test wherein the inflator when placed directly in a fire cannot become a projectile upon ignition of the stored propellant.
To pass this test, inflator manufacturers have devised ways to balance the exhausting gases to create a “thrust neutral” or “zero thrust” inflator.
In U.S. Pat. No. 7,938,443 B a patent entitled “Shipping Safe Inflator For An Airbag Module” discloses a distal end portion of an inflator with a thrust balancing feature having a plurality of elongated secondary apertures with deflection vanes open to exhaust the gases in a thrust balance configuration. This distal end can discharge gases exiting along the axis through the primary discharge opening and the elongated secondary passages redirect part of the flow longitudinally aft oppositely directed to cancel thrust and has a plurality of radially oriented openings to exhaust more of the gas radially in such a fashion the inflator has no thrust capability due to inadvertent ignition.
Others have simply designed inflators with a plurality of holes radially around the circumference of a housing to create a thrust neutral inflator. This technique is most simple and easy to employ in passenger side inflators and other applications wherein the inflator is stored in a housing assembly.
In side curtain airbags, the inflator is generally not in a module housing, but is secured directly onto the vehicle along with the airbag curtain connected via a hose or tubing assembly. In this case, the inflator needed to be designed in such a way that the propellant gases are captured to fill the curtain. Ideally the gases are not lost or vented to atmosphere to achieve a thrust neutral condition when in use. This is true because to vent large amounts of the inflation gases means even more propellant must be used so the remaining captured gases are sufficient to fill the airbag. Accordingly, to insure the inflator achieves a thrust neutral balanced exhaust when exposed to fire during shipping and storage, but when assembled for normal use this safety feature does not waste the inflation gases a new a superior way to manufacture a thrust neutral inflator assembly is needed. Preferably, the new way is accomplished in a cost efficient and very reliable way. These and other beneficial objectives are satisfied by the present inventive design described herein.